There have so far been proposed a wide variety of video apparatus for replaying moving picture by using compressed data.
According to the recommendation by Moving Picture Expert Group, hereinafter simply referred to as “MPEG”, of International Organization for Standard/International Electro-technical Commission Joint Technical Committee 1 Sub Committee 29, hereinafter simply referred to as “ISO/IEC JTC1 SC29”, three types of compressed data are defined for moving pictures, that is, Intra-coded pictures, Predictive-coded pictures, and Bidirectionally-coded pictures, hereinafter simply referred to as “I-pictures”, “P-pictures”, and “B-pictures”, respectively.
I-pictures are MPEG pictures that are intra-coded, that is, not coded differentially with respect to other pictures, such as P-pictures and B-pictures, and are obtained by compressing one frame data using spatial compression technique such as Discrete Cosine Transformation, hereinafter simply referred to as “DCT”. P-pictures are MPEG pictures that are forward predicted from previous I-pictures or P-pictures using the inter-frame prediction coding technique. B-pictures are MPEG pictures that are Bidirectionally predicted from a combination of a preceding reference frame pictures or field pictures and a following reference frame pictures or field pictures (each reference is either an I-picture or a P-picture), using the inter-frame prediction coding technique. Since B-pictures are predicted as mentioned above, a B-picture is decompressed after decompressing the preceding I-picture or the preceding P-picture, and the B-picture is stored after storing the preceding I-picture or the preceding P-picture which is used to decompress the current picture in the frame memory as shown in FIG. 20. Therefore, the order of storing the B-picture shifts backward as compared with that of the original picture.
Generally, the compressed data are divided into a plurality of groups of pictures, hereinafter simply referred to as “GOP”, in order to enable the random-access which can read each GOP in any order. Each GOP includes at least one I-picture and this I-picture may be inserted between the pictures of the other type at a regular interval.
The decompression process is performed in sequence by the stored data as shown in FIG. 17. After the decompression process is performed, the replay process is performed in sequence by the originally stored data rearranged in original order.
In order to start the replay process, an arbitrary data of either a P-picture or a B-picture, such as the data of the B-picture B13, is designated by a control mean. However, the B-picture B13 cannot be decompressed without the data of the P-picture P14, since the B-picture B13 has Bidirectionally-predicted data.
Therefore, to obtain the data of the P-picture P14, the replay process is performed from the I-picture 12 included in the same GOP containing the designated B-picture B13, or from other I-picture included in the next GOP. A method of the replay starting from a designated picture is disclosed in the Japanese Patent Laid-Open Publication No. 8-205083 in which a decompression process is performed while a still picture is displayed on a display monitor. In the case of this prior art, the decompression process is performed from the I-picture of the GOP which includes the designated picture. Then the following P-pictures and/or B-pictures are decompressed until the decompression process reaches to the designated picture. As shown in FIG. 18, the designated picture is displayed until the following picture of the designated picture is decompressed.
However, since the apparatus for decompressing the compressed data of prior art has to decompress the previous I-picture and all of the P-pictures and the B-pictures that are included in the GOP containing the designated picture, it is required to take time interval to replay the designated picture. In addition, because of performing the decompression process of each fame data (i.e. the previous I-pictures and the previous P-pictures necessary to decompress the designated picture) synchronously with the timing of displaying the picture, hereinafter simply referred to as “display timing”, the decompression process of pictures cannot be started until the next display timing, it is required to take time interval for starting the decompression of the designated picture.
Furthermore, the apparatus for decompressing the compressed data of the prior art requires frame memories for storing I-pictures, P-pictures and B-pictures used in the decompression process and for storing the frame data of a picture to be displayed while each compressed data is decompressed. As a result, such apparatus tends to be large in scale and expensive.